spiritman,
First you have to remember who Jesus was:
Deu 18:15 The LORD thy God will raise up unto thee a Prophet from the midst of thee, of thy brethren, like unto me; unto him ye shall hearken;
Moses said another law giver would come. Jesus was that law giver. Jesus had the authority to change the law. His disciple's were braking the Sabbath by going through the field picking wheat and eating it. Telling a man to carry a bed roll on the Sabbath was also forbidden by the law of Moses. Yet Jesus is showing the people that mercy trumps the law. In the sermon on the mount, Jesus is putting the cap stone on the Law of Moses. He is making the law so hard to follow that no one will be able to say they can be justified by it again. (Like Paul did). Don't believe he was talking old covenet?:
Mat 5:23 Therefore if thou bring thy giftG1435 to the altar, and there rememberest that thy brother hathG ought against thee;
Mat 5:24 Leave there thy giftG1435 before the altar, and go thy way; first be reconciled to thy brother, and then come and offer thy gift.G1435
Check out gift G1435:
G1435
δῶρον
dōron
do'-ron
A present; specifically a sacrifice: - gift, offering.
He is talking to these people about sacrifices on the alter. Is that not old covenant? He is giving these people some solid principles that we can surely use but remember who He is talking to, the house of Isreal. He is talking law. And in that capasity He was in the place of Moses. Thats why He got angry at the temple. Moses would have flipped out too.
hope that helps.